This invention relates to a repair method for a blade of a turbomachine. More particularly, this invention relates to a repair method in which at least a partial area of a leading edge of the blade is removed.
Turbomachines according to the present invention are, for example, fans, compressors, pumps and blowers of the axial, semi-axial and radial type which can be operated with gaseous or liquid working media. The turbomachine according to the present invention can comprise one or several stages, each with one rotor and one stator, in isolated cases, the stage may also consist of a rotor only. The rotor features a number of blades which are connected to the rotating shaft of the turbomachine and impart energy to the working medium. In accordance with the present invention, the rotor can be shrouded or shroudless at the outer blade end.
The stator may consist of a number of stationary blades with fixed or free blade ends on the casing side as well as on the hub side. The rotor drum and the blading are usually enclosed by a casing; however, in accordance with the present invention, a casing is dispensable, for example in the case of ship or aircraft propellers.
The turbomachine may also be provided with a stator upstream of the first rotor, a so-called inlet guide vane assembly. Instead of being fixed, at least one stator or guide vane assembly can be rotatable to change the angle of incidence. Such variation can, for example, be accomplished by a spindle accessible from outside of the annulus. Alternatively, multi-stage versions of the turbomachine in accordance with the present invention may have two contra-rotating shafts, with the rotor blade rows rotating in opposite directions from stage to stage. Here, stators do not exist between subsequent rotors. Furthermore, the turbomachine according to the present invention may alternatively have a bypass configuration, in which a single-flow annulus divides into two concentric annuli behind a certain blade row, with the concentric annuli again comprising at least one further blade row.
The efficiency and operating stability of turbomachines, such as fans, compressors, pumps or blowers, are subject to considerable operational degradation which necessitates modification or rework of components of the turbomachine which have seen extended service use. As a further aspect, component wear leads to increased vibrational load, as a result of which the originally expected life of blades and disks is not achievable.
Therefore, in adverse cases, the stability margin of the turbomachine provided in the original design of the blading may partly or fully be lost or the actual life of blades and/or disks may be shortened. The reason for this is, for example, a growth of the radial running gaps, in particular at the blade tips of rotors, which results in an intensification of the detrimental flow across the radial gaps from the pressure to the suction side of each blade.
Basically, subsequent improvement of the flow field can be achieved by applying specific measures to either the casing or the blading. One possibility is a special structuring of the casing in the running path of the blades by so-called ‘casing treatments’.
As regards the repair of blades, it is known from the state of the art to grind out the damaged areas, in particular to avoid notch effects. However, these standard measures frequently lead to a significant decrease in the performance of the turbomachine. In addition, blades which shall be repairable by such methods must be oversized considerably to provide sufficient repair stock. A repair method is known from Specification DE 197 12 868 C1, for example.